1. Field of the Invention
This invention relates to a system for generating a gait (walking pattern) for a legged mobile robot, more particularly to a system for generating a gait (walking pattern) for a legged mobile robot using biped locomotion, which enables the robot to satisfy the conditions for dynamic equilibrium and achieve stable walking even when walking on uneven terrain not constituted by a single plane.
2. Description of the Prior Art
Legged mobile robots, in particular legged mobile robots using biped locomotion, are taught by Japanese Laid-open Patent Publication Nos. 62 (1987)-97005 and 63(1988)-150176. An in-depth discussion of robot control, including the control of legged mobile robots, can be found in Robotics Handbook, Robotic Society of Japan, Oct. 20, 1990.
As explained in detail starting from page 347 of the Robotics Handbook, the concept of ZMP (zero moment point) has been introduced into the control of legged mobile robots, and the control is conducted by determining the gait (walking pattern) such that the ZMP follows a target trajectory. Here, the term ZMP means a point on the ground at which the horizontal moments around the x and y axes produced by the ground reaction force is zero irrespective of whether or not the vertical moment around the z axis arises. A required condition for dynamic force equilibrium in this case is that the ZMP be located inside a minimum convex polygon including the ground surface. Moreover, the margin of stability of the gait (walking pattern) can be optimized by designing it such that the ZMP is positioned as close as possible to the center of the minimum convex polygon including the ground surface.
The ZMP is, however, a concept that holds only with respect to a single plane, more specifically, a single horizontal plane. The ZMP concept cannot be applied to the design of a gait for a robot which is to walk across uneven terrain such as inclined terrain of varying gradient or the like because under such circumstances the robot will sometimes be in simultaneous contact with two or more ground planes that differ in height or the direction of their normals.